1. Field of the Invention
The present invention relates to a signal transmission circuit and a signal transmission system.
2. Related Art
In a system having a pulse clock of GHz band, it is not possible to extend a wiring due to resistance loss, delay and loss by RC or dielectric loss. However, a long wiring becomes more and more important in an inter-block communication or the like, for example, high-speed transmission such as 100 Gbps in metal wiring is required for a LAN cable.
An inter-block wiring can be considered as a transmission line represented by a distributed constant circuit, and it is possible to correspond to high-speed transmission predicting loss characteristic by a transmission applying a pre-emphasis or a de-emphasis or by a correction by adjusting a waveform level by an equalizer.
An equalizer is, for example disclosed by JP-A-2006-191355, configured to be π type in that a resistance and a condenser are connected in parallel between transmission lines and that a resistance and an inductor are connected to Input/Output of the circuit by this parallel connection and a ground respectively. In this case, a condenser having low impedance with respect to a compensation bandwidth and an inductor having high impedance with respect to an amends band are used.
In an equalizer or a pre-emphasis, it is accordingly possible to control a waveform as long as a line with a bit width has the same structure and waveform disorder is constant, and in case of a LAN cable, it is possible to transmit 100 m at 1 Gbps.
However, for making these waveform disorders with a transistor circuit of output stage of a transmitting side, a transistor having a frequency characteristic of one digit higher than a clock signal is required. Compared with this, since a passive circuit does not basically have a nonlinearly frequency characteristic if a parasitic characteristic is decreased, it does not require a sophisticated transistor circuit technology and does not consume electric power actively. Therefore, high-speed transmission is allowed only by inserting the passive circuit into a signal system of each type of circuit.
Next, as a method for improving a characteristic on a receiving side, there is a de-emphasis as a representative example. In the de-emphasis, a crosstalk signal is superimposed in a halfway when waveform amplitude on the receiving side decreases, which causes an incorrect operation. To reduce this crosstalk signal, it is only necessary to reduce an expansion of an electromagnetic wave of the transmission line, and there is a coaxial cable as a representative example.
Further, there is a reflection as a phenomenon which causes a trouble in the transmission line. In the transmission line, an energy which returned to the transmission line reflecting at a discontinuous point repeats a multiple reflection by reflecting again at the discontinuous point on a return side, and when sympathetic vibration etc. occurs, it becomes a totally unpredictable transmission waveform. Therefore, it is required to prevent an occurrence of the multiple reflections.